A6M spec calls for high protection and heavy firepower

It is one thing to build a ship-board naval fighter with good range with some provision for pilot protection. It is another thing to build a land-based naval fighter capable of striking Clark Field from Formosa, or Guadalcanal from Rabaul. It was 3 months before the Japanese established a field at Buin to cut the range to the 'Canal. P-38s ran the return attack to Bougainville carrying one 165 gal and one 330 gal drop tanks. Operation Vengeance was a big deal, but Zeros flew to Guadalcanal regularly, past coast-watchers and into radar.
 
Interesting. I doubt the IJN would want to give up the range but it would double the firepower.

It would kill the range. Would have to redesign the wing and fuselage to get enough fuel tankage
3a97ea26389369afbfbd6347ef8ac4c0.png
 
On a paralel note regarding the Kasei, i swear i have read a snippet somewhere from one of you very knowledgeable gents regarding the J2M Raiden, the XP-42 and their extended shaft- close cowling problems, the gent said, presumably when refering to the type of cowling tested on XP-42, that they (Mitsubishi) used #2 - or was it #3?- when they should have used #5. I have looked at some XP-42 pics on the web, can i ask which one is #5 and which one is #2, though possibly i think i know which one is #2 as it looks similar to...well, the one on Raiden. Is #5 the one that looks almost normal and make the P-36 look familiar again?
https://crgis.ndc.nasa.gov/historic/XP-42
http://www.airwar.ru/enc/fww2/p42.html

Thank you.
 
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It is one thing to build a ship-board naval fighter with good range with some provision for pilot protection. It is another thing to build a land-based naval fighter capable of striking Clark Field from Formosa, or Guadalcanal from Rabaul. It was 3 months before the Japanese established a field at Buin to cut the range to the 'Canal. P-38s ran the return attack to Bougainville carrying one 165 gal and one 330 gal drop tanks. Operation Vengeance was a big deal, but Zeros flew to Guadalcanal regularly, past coast-watchers and into radar.
I believe they started flying from Buka, about 400nm, in late August 1942. Buin i think was even closer at 300nm (gotta recheck in Prados again).
 
even the spinners caused cooling trouble on some aircraft, like was removed from the Helldiver and XF6F-3 Hellcat
 
even the spinners caused cooling trouble on some aircraft, like was removed from the Helldiver and XF6F-3 Hellcat

I have a book on the Hellcat that states that everyone but the aerodynamicists were happy when the spinners were removed to ease maintenance. Aerodynamicists are just the people that make for faster airplanes. The fastest Wildcat had a spinner, and was faster than a Zero. The fastest Bearcat, and the fastest piston engine aircraft has a spinner.
 
The XP-42 featured cooling fan in most, if not all of if it's iterations. The version with short prop shaft is depicted here. It is possible that big spinners need fans to help out with cooling? Fans don't work for free, the BMW 801 used around 3.5% of power for the fan.
One (or more?) iteration of the powerplants of the XP-42 included the individual exhaust stacks in very much Fw 190 vogue, tested in winter of 1941/42.
Allies didn't needed Faber to make it's mistake in order to came out with a much better installation for their engines.

How hard is it to add another row of cylinders to the Nakajima Sakae?
Could the Homare be developed in the late 1930s?
https://en.wikipedia.org/wiki/Nakajima_Homare

A million dollar question :)
Sakae was already with two rows of cylinders.
The 1st two-row radial by Nakajima that I'm aware of is the Ha-5 from 1937. Power 890 HP at 4700 m, 950 HP for take off, 1260 mm diameter, 625 kg. Later developed into Ha-41 that powered eg. Ki-44, 1260 HP at 3700m, 1260 HP for take off, more RPM allowed, just 5 kg heavier, produced from 1940. 1st flight of the Ki 44 was in August 1940, or almost a year and a half after the Zero.
Ha-109 was a further development of the Ha-41, featuring a bigger superchager, with two-speed gearing and neccesarry strengthening. Power at 5200 m was 1220 HP, at 2100 M was 1440, and 1500 HP for take off. Weight 720 kg.
Our Zero with Ha-5/Ha-41/Ha-109 would've been a compettitive machine.

But to your question - let's say Nakajima develops an 18 cyl engine with same bore and stroke as the Sakae, on same technological level. That would've give around 1280 HP in 1st versions, and 1400+ in mid war.
 
Is #5 the one that looks almost normal and make the P-36 look familiar again?
https://crgis.ndc.nasa.gov/historic/XP-42

It is the 03/43 and 04/13/45 model, pictured with all-flying tailplane.


I believe they started flying from Buka, about 400nm, in late August 1942. Buin i think was even closer at 300nm (gotta recheck in Prados again).

My oldsheimer memory suggests October for Buin and December for Buka.

A million dollar question :)
Sakae was already with two rows of cylinders.
But to your question - let's say Nakajima develops an 18 cyl engine with same bore and stroke as the Sakae, on same technological level. That would've give around 1280 HP in 1st versions, and 1400+ in mid war.

Could not the 18 cyl Sakae be called the Homare/NK9 and would it not have problems with difficult construction/maintenance and overheating/lack of reliability and failure to produce advertised power at altitude, but achieve a very small diameter?
 
Could not the 18 cyl Sakae be called the Homare/NK9 and would it not have problems with difficult construction/maintenance and overheating/lack of reliability and failure to produce advertised power at altitude, but achieve a very small diameter?

We can call it any way we are pleased :)

The Homare was trying to make 2900-3000 rpm, and it needed a technological breakthrough (perhaps too strong a word, but anyway) in form of dynamic ballancers to do that, plus the steel crankcase. More rpm = more power, at all altitudes, if enegy can handle it of course. The use of water/alcohol injection was there to facilitate increase of boost; more boost = more power.
Without water/alc injection and at 2900 rpm, power was at around 1850 HP; at 3000 rpm + w/a injection it was supposed to be at 2050 HP.
Late versions (Mod 21, 22 - those making 3000 rpm) were also with compression ratio increased from 7:1 to 8:1. You've guessed it - greater compression ratio = small increase of power. Here it might be the Japanese make a big mistake - increasing the compression ratio increases stress on engine more than increse in RPM, and far more than increase of boost due to hi-oct fuel available or w/a injection. Greater stress = lower reliability.
Homare was to make 1600 HP+ at 20000 ft in it's latest iterations with it's 1-stage SC, a very good value for 1945, even though most 2-stage engines were much better above 20000 ft.

The Sakae was turning 2600-2700 rpm in it's latest versions, 2500-2600 rpm in earlier. Dead reliable while doing it. Aluminium crankcase. Compression ratio 7:1 in most of the versions by mid-war. Rumor is that it was using water/alc injection by late war, the engine power figures don't lend plenty of credit to those rumors. Such a 'low tech Homare' will probably be very reliable, but not very powerful.
 
Thanks Tomo and Leo for the XP-42 details.

Well, looks like we go back to either an early Homare and/or a 18 cylinder Zuisei. According to japanese wiki, Homare was initially planned to run on 100 octane fuel, but they had to redesign it for MW-50 injection as 100 octane fuel became clearly unavailable. Initially, using standard Sakae tech the estimated output was 1300HP, not exactly sure which Sakae this one is but likely it's Sakae-12, so it goes from 950HP for 14cyl to 1300HP for 18 cyl. If you use the Sakae-21 tech then that should go around 1500HP no? It should be the same story with 14 cyl Zuisei / ATL 18 cyl Ryusei. The Zuisei was designed in 1936, was definitely flying in 1938 and possibly earlier in 1937 on one of the Mistubishi F1M prototypes. Don't have the exact data, but much the same applies with Sakae, it was definitely flying in late 1938 (on the Ki-43 prototype)

So if you somehow have parallel programs for 18 cylinders Zuisei and Sakae in addition to the OTL 14 cyl ones, they should be available in 1939 - 1940.

Btw, back to the Kasei or Shinten for this ATL super-Zero, i like the cowling of the N1K1, note, just the cowling, not the contrarotating prop or extended shaft! Looks similar to one of the XP-42 configurations. Would look good on a Raiden, or on a super-Zero.
 

trurle

Banned
I must point out what before capture of Dutch East Indies the Japanese were too short of rubber to try self-healing tanks on wide scale. They struggled to get enough rubber even for all the wheels (notably Type 95 75mm gun in 1935 was designed from the beginning in wooden wheel and rubber wheel variants). I remember in 1942 some Japanese aircraft (do not remember model) fuel tanks were coated in 5mm rubber (not truly self-healing tanks) as rapid production upgrade using a captured rubber stocks.

Regarding Mitsubishi Kasei: fighter using Mitsubishi Kasei was Mitsibishi J2M. Though potent, its development was a disaster mostly because of poorly suitable Kasei engine. Solving all the quirks took about 2.5 years IOTL.
 
Though potent, its development was a disaster mostly because of poorly suitable Kasei engine. Solving all the quirks took about 2.5 years IOTL.

Although there was a suitable Kasei, they chose not to use it. They put development on hold to develop the Zero with revisions, and then to add corrections to the revisions, and so on. They could only do one thing at a time. Monthly Jack production was usually 1 or 2, soaring in one month to 44, and falling again. They built 2435 Bettys and the engines were just fine.
 

trurle

Banned
Although there was a suitable Kasei, they chose not to use it. They put development on hold to develop the Zero with revisions, and then to add corrections to the revisions, and so on. They could only do one thing at a time. Monthly Jack production was usually 1 or 2, soaring in one month to 44, and falling again. They built 2435 Bettys and the engines were just fine.
G4M "Betty" was 2-engine bomber of much lower speed. Requirements for drag and reliability of Kasei engine on G4M "Betty" were obviously much lower (by factor of 2-4) compared to J2M "Jack" single-engine interceptor. It was the low-drag cowling for fighter installation of Kasei engine which caused majority of the trouble. Requirements for reliability (highly dependent on engine temperature) and drag were strongly conflicting, therefore progress was slow.

Actually Japanese needed nickel superalloys to break the cooling/drag trade-off of Kasei engines, but according to
http://www.tms.org/superalloys/10.7449/1984/superalloys_1984_399_419.pdf

all early superalloys needed a lot of Chromium for oxidation resistance.
N60A: 17% Cr
HS21: 20-30% Cr
X40: 22% Cr

Unfortunately to Japan, the lack of chromium was crippling. Japanese were even forced to eliminate just 1% of chromium contents in AP shells, even knowing the penetration power will suffer. I suspect all the available chromium was consumed by makers of corrosion-resistant plating of naval equipment.

Translating from Japanese Wikipedia:
https://ja.wikipedia.org/wiki/一式機動四十七粍速射砲

"The main cause of the penetration performance shortage of armor-piercing artillery slugs was the material of the slugs. For example, typical Japanese armor plate did not contain chromium (Cr contents was 0.006-0.015%, compared to 1% Cr contents of German of American armor). The Army was also aware of the inferior quality of Japanese AP slugs. Test slugs for Japanese cannons made of tungsten-chromium steel were found to be equivalent to foreign slugs in penetration performance though."
 
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G4M "Betty" was 2-engine bomber of much lower speed. Requirements for drag and reliability of Kasei engine on G4M "Betty" were obviously much lower (by factor of 2-4) compared to J2M "Jack" single-engine interceptor. It was the low-drag cowling for fighter installation of Kasei engine which caused majority of the trouble. Requirements for reliability (highly dependent on engine temperature) and drag were strongly conflicting, therefore progress was slow.

The requirements regarding drag and reliability are the same. Drag reduction imparts speed and range, and speed and range are important even in bombers and recce aircraft. The Betty got a prop spinner in 1942. The Nakajima Ki-44 had a more conventional looking engine installation but also went through some aerodynamic refinement. The Vultee P-66 went through a stage of silliness that delayed its production, and the XP-42, of course, underwent development for years before discovering the right way, way, way too late to be of value. The FW-190 went through the silly stage for a relatively short time before its remarkable refinement.


I had a '56 Buick. I love chrome. You can't make one without it.
 

trurle

Banned
Drag reduction imparts speed and range, and speed and range are important even in bombers and recce aircraft. The Betty got a prop spinner in 1942. The Nakajima Ki-44 had a more conventional looking engine installation but also went through some aerodynamic refinement. The Vultee P-66 went through a stage of silliness that delayed its production, and the XP-42, of course, underwent development for years before discovering the right way, way, way too late to be of value. The FW-190 went through the silly stage for a relatively short time before its remarkable refinement.
Please do not "mix apples and oranges".
Drag is roughly proportional to SQUARE of speed multiplied to frontal area. Therefore, 650km/h J2M will have ~230% of engine pod drag compared to 430km/h G4M bomber. And drag power is proportional to CUBE of speed.
Actually without cowling (form factor 0.8), Kasei engine exposed to 650 km/h slipstream would lose ~8200 hp for its own drag at sea level. Even with perfect cowling (no air inlet) the loss would still be about 200 hp. So Japanese designers of J2M took Kasei engine which has too large frontal area for high-speed interceptor..made the barely sufficient air inlet to minimize drag..found the engine parts are overheating..and spent next 2.5 years trying to properly direct the paltry amount of cooling air to the most overheating parts. Actually, everybody in world had similar problems in period, Japanese were only particularly badly restricted in search of solution by worse quality of available alloys.

Speaking bluntly (and not very accurately), all the radial engines (including Mitsubishi Kasei) were obsolete as soon as speed of aircraft reached 600 km/h. They spent the cooling air too wastefully because length of heat transfer section was inherently too short. On the other hand, V-engines allowed much more efficient heat transfer, although the problem of heat transfer between front and back cylinders needed some complicated technological solutions (typically involving multiple liquid cooling circuits as in Packard V-1650 Merlin used on P-51).

The requirements regarding drag and reliability are the same.
Regarding reliability of Kasei engine: G4M "Betty" was designed from very beginning to fly after one engine fails. Actually it was common for damaged G4M to return from missions on one engine. If J2M Kasei engine fails, with 90% probability aircraft falls to sea and lost. If G4M Kasei engine fails, with 90% probability aircraft returns to base. Feel the difference in reliability specs for the same engine on different aircraft?
 
Please do not "mix apples and oranges".
Drag is roughly proportional to SQUARE of speed multiplied to frontal area. Therefore, 650km/h J2M will have ~230% of engine pod drag compared to 430km/h G4M bomber. And drag power is proportional to CUBE of speed.
Actually without cowling (form factor 0.8), Kasei engine exposed to 650 km/h slipstream would lose ~8200 hp for its own drag at sea level. Even with perfect cowling (no air inlet) the loss would still be about 200 hp. So Japanese designers of J2M took Kasei engine which has too large frontal area for high-speed interceptor..made the barely sufficient air inlet to minimize drag..found the engine parts are overheating..and spent next 2.5 years trying to properly direct the paltry amount of cooling air to the most overheating parts. Actually, everybody in world had similar problems in period, Japanese were only particularly badly restricted in search of solution by worse quality of available alloys.

Is that ~8200 HP value a typo?
Do we actually Know what kind of special alloys were used on European or US radial engines, that were not used on Japanese?

Speaking bluntly (and not very accurately), all the radial engines (including Mitsubishi Kasei) were obsolete as soon as speed of aircraft reached 600 km/h. They spent the cooling air too wastefully because length of heat transfer section was inherently too short. On the other hand, V-engines allowed much more efficient heat transfer, although the problem of heat transfer between front and back cylinders needed some complicated technological solutions (typically involving multiple liquid cooling circuits as in Packard V-1650 Merlin used on P-51).

There was plenty of radial-engined aircraft that went well beyond 600 km/h, and some also went beyond 700 km/h. Being reliable while doing it.
Care to elaborate a bit on multiple liquid cooling circuits on the Merlin Mustang (and other that used it presumably), apart from intercooler cooling circuit?

Regarding reliability of Kasei engine: G4M "Betty" was designed from very beginning to fly after one engine fails. Actually it was common for damaged G4M to return from missions on one engine. If J2M Kasei engine fails, with 90% probability aircraft falls to sea and lost. If G4M Kasei engine fails, with 90% probability aircraft returns to base. Feel the difference in reliability specs for the same engine on different aircraft?

The G4M was required to fly a multi-hundred miles missions, including over water, so having a relaxed requirement for engine reliability does not seem to hold water. I don't think there is abundance of evidence that Kasei on G4M was failing on regular bases either.
 

trurle

Banned
Is that ~8200 HP value a typo? Do we actually Know what kind of special alloys were used on European or US radial engines, that were not used on Japanese?
Not a typo. It is just a number showing what too-wide Kasei engine without cowling cannot reach 650km/h even without additional airframe to carry - because drag power would exceed the available engine power. About alloys - these nickel superalloys were US-developed starting from 1940, and you can assume the British also used them with the US-British tech cooperation level of the era. My sources says these alloys were critical for the turbochargers development, but i do not know to which extent these alloys were used in other parts of the engines. Most likely the introduction was very gradual. I do not have any specific reference on Japanese alloys of era (may be simplest way is actually to get metal sample of Japanese engines and get X-ray spectrum - i doubt any documentation survived, so rely on proximal proof.) On the other hand, i remember Soviet publication of 1941 mentioning novel turbochargers metal rapidly "burning through" - therefore it is likely Soviets also did not have superalloys.
There was plenty of radial-engined aircraft that went well beyond 600 km/h, and some also went beyond 700 km/h. Being reliable while doing it.
Care to elaborate a bit on multiple liquid cooling circuits on the Merlin Mustang (and other that used it presumably), apart from intercooler cooling circuit?
The 600-730 km/h is extreme for radial engines. They can still work, but other types of engines would work much better. Regading "multiple cooling circuits" of P-51, i meant exactly intercooler. Sorry for ambiguous wording.

The G4M was required to fly a multi-hundred miles missions, including over water, so having a relaxed requirement for engine reliability does not seem to hold water. I don't think there is abundance of evidence that Kasei on G4M was failing on regular bases either.
Your logic can be reversed too. J2M was flying only short interception mission, over or close to land, because the reliability of the single-engine aircraft with the given engine reliability was much worse compared to 2-engined, long-range G4M. Also, if you look on wartime photos thoroughly, many G4M cowlings of Kasei engine have ear-like additional inlets (one or sometimes even two) over the top of cowling. These inlets were always missing on J2M engine cowling - due to high drag at high speed, as i suspect.
 
Not a typo. It is just a number showing what too-wide Kasei engine without cowling cannot reach 650km/h even without additional airframe to carry - because drag power would exceed the available engine power. About alloys - these nickel superalloys were US-developed starting from 1940, and you can assume the British also used them with the US-British tech cooperation level of the era. My sources says these alloys were critical for the turbochargers development, but i do not know to which extent these alloys were used in other parts of the engines. Most likely the introduction was very gradual. I do not have any specific reference on Japanese alloys of era (may be simplest way is actually to get metal sample of Japanese engines and get X-ray spectrum - i doubt any documentation survived, so rely on proximal proof.) On the other hand, i remember Soviet publication of 1941 mentioning novel turbochargers metal rapidly "burning through" - therefore it is likely Soviets also did not have superalloys.

My take on this is that you're trying to apply the fact, that turbochargers need better alloys*, on the engines' 'power sections'. Both Soviets, Germans and Japanese were able to get their engines make 1700+ HP by 1943-44, granted some more reliable than others. The ordinary Kasei was wider than BMW 801 by less than 5%.
BTW - Americans said that Raiden was a 400+ mp/h machine.

*unless the turbine blades are hollow, like the Germans did with BMW 801J installation

The 600-730 km/h is extreme for radial engines. They can still work, but other types of engines would work much better. Regading "multiple cooling circuits" of P-51, i meant exactly intercooler. Sorry for ambiguous wording.

The 600 km/h value was soundly beaten by a radial-powered XF4U-1 and Fw 190 by 1940/41, touching 650 km/h actually. Britain followed the suit with Centaurus-powered Tornado, again well above 600 km/h, despite the outdated installation of the engine and wing profile. La-7 and later series of La-5FN were above 650 km/. By 1945, Allied radial-engined fighters were above 700 km/h - Tempest II, Sea Fury, Yak-3U, F4U-4, F8F-1.
All of this is before we say: P-47.

Your logic can be reversed too. J2M was flying only short interception mission, over or close to land, because the reliability of the single-engine aircraft with the given engine reliability was much worse compared to 2-engined, long-range G4M. Also, if you look on wartime photos thoroughly, many G4M cowlings of Kasei engine have ear-like additional inlets (one or sometimes even two) over the top of cowling. These inlets were always missing on J2M engine cowling - due to high drag at high speed, as i suspect.

Those inlets were ram-air inlets for the carburettor. JM2 was with those inlets, but they were under the long cowling, the 'fresh' air 1st encountering the spinner, than the cooling fan, then entered the inlet. Japanese were too smart for their own good here, similar to what BMW did with the 801 - ram air needs to be undisturbed as much as possible, and the inlet as wide as possible.
The reason why J2M flew short missions was that it was designed as short range interceptor, with small internal fuel tankage for the power installed.
 
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